Like much of the nation’s infrastructure, the condition of our nation’s bridges has come under increased scrutiny. Some of these spans are icons that are world renowned. They can be a couple of thousand feet long and carry thousands of vehicles per day. Or they can be hidden deeply in woodlands or rural oases. No two are alike.
Although bridges vary in size and purpose, one fact has become painfully clear: Many are in need of major repairs and restoration. One of the 70,000 bridges that the U.S. Federal Highway Administration had called “structurally deficient” links the tiny private Grove Island in Biscayne Bay just south of Miami to the Florida mainland. The 800-foot-long Grove Isle Bridge is the only lifeline for the tiny Grove Isle Hotel & Spa. The U.S. Coast Guard and Florida Department of Transportation own the bridge while the Grove Island Condo Association maintains it.
Much of the six-month-long, $2.3 million project involved repairing the concrete on the underside of the bridge deck. This included repairing the reinforcement and patching. Workers also sealed the deck and installed new lighting.
After removing delaminated concrete from the underside of the bridge slab, workers used hydrodemolition on the exposed concrete areas with water blasts up to 4000 psi to reach solid, sound concrete. Then they cleaned the steel rebar and coated them with Mapefer 1K, an anti-corrosion and bonding mortar by Mapei, a manufacturer of concrete restoration products in Deerfield Beach, Fla.
Ontario, Calif.-based Fibwrap Construction Inc., the general contractor, formed up the underside areas and pumped in Planigrout 712, a nonshrinking cementitious construction grout. The mix contains a corrosion inhibitor and silica fume, as well as a special blend of aggregate, plasticizers, and water-reducing agents. Repair mortar was hand-applied to smaller areas. Once it dried, its light gray color matched the existing concrete surface to give a uniform appearance.
The crew used a full-depth repair mortar on the upper sections of the bridge where sidewalk curbs meet the traffic surface. This product, Planitop FS, is pumpable and works on deep repairs that require rapid return to service.
After repairs were complete, workers cleaned and waterproofed nontraffic areas of the bridge with a cementitious liquid waterproofing membrane that will protect the bridge from chemical attack by deicing salts, sulfates, chlorides, and carbon dioxide that lead to deterioration.
If or when there is a need for future repairs, it will not come as a surprise, thanks to an innovative monitoring system. Researchers at the University of Miami placed wireless sensors at strategic points on the bridge. By recording concrete alkalinity levels, vibrations, and sound waves, they will detect cracks and deficiencies.
Part of a new effort to better monitor U.S. bridge safety, this technology will help bridge owners and transportation departments monitor and predict future structural problems. Owners and agencies will be alerted to critical repairs and renovations.